Wireless communication systems are well known in the art. Generally, such systems comprise communication stations, which transmit and receive wireless communication signals between each other. Depending upon the type of system, communication stations typically are one of two types: base stations or wireless transmit/receive units (WTRUs), which include mobile units.
The term base station as used herein includes, but is not limited to, a base station, Node B, site controller, access point or other interfacing device in a wireless environment that provides WTRUs with wireless access to a network with which the base station is associated.
The term WTRU as used herein includes, but is not limited to, a user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. WTRUs include personal communication devices, such as phones, video phones, and Internet ready phones that have network connections. In addition, WTRUs include portable personal computing devices, such as PDAs and notebook computers with wireless modems that have similar network capabilities. WTRUs that are portable or can otherwise change location are referred to as mobile units.
Typically, a network of base stations is provided where each base station is capable of conducting concurrent wireless communications with appropriately configured WTRUs. Some WTRUs are configured to conduct wireless communications directly between each other, i.e., without being relayed through a network via a base station. This is commonly called peer-to-peer wireless communications. WTRUs can be configured for use in multiple networks with both network and peer-to-peer communications capabilities.
One type of wireless system, called a wireless local area network (WLAN), can be configured to conduct wireless communications with WTRUs equipped with WLAN modems that are also able to conduct peer-to-peer communications with similarly equipped WTRUs. Currently, WLAN modems are being integrated into many traditional communicating and computing devices by manufacturers. For example, cellular phones, personal digital assistants, and laptop computers are being built with one or more WLAN modems. Accordingly, there is an increasing need to facilitate communications among such WTRUs with WLAN modems. For instance, it would be desirable if a first user of a PDA equipped with a WLAN modem could share data, such as a phone book, with a second user having a cellular phone equipped with a WLAN modem locally, without going through a telecommunications network.
A popular wireless local area network environment with one or more WLAN access points, i.e., base stations, is built according to the IEEE 802.11b standard. The wireless service areas for such WLANs are often restricted to geographic areas, commonly referred to as “Hot Spots”. Such wireless communication systems are advantageously deployed in a wide variety of locations such as airports, coffee shops, and hotels to name just a few contexts. Access to these networks usually requires user authentication procedures. Protocols for such systems are presently being standardized in the WLAN technology area. One such framework of protocols is the IEEE 802 family of standards.
There are two prevalent ways to implement wireless communications in WLAN and other networks: 1) an infrastructure mode; and 2) an ad hoc mode. FIG. 1A illustrates an infrastructure mode, where WTRUs conduct wireless communications via a base station 54 that serves as an access point to network infrastructure 16. The base station 54 is shown as conducting communications with WTRU 18, WTRU 20, WTRU 22, WTRU 24, and WTRU 26. There are no direct intercommunications between the WTRUs illustrated in FIG. 1A. The communications are coordinated and synchronized through the base station 54. Such a configuration is also called a basic service set (BSS) within WLAN contexts.
In contrast to the infrastructure mode, the ad hoc mode does not use network infrastructure. The ad hoc mode operates with peer-to-peer communications and is also called “independent BSS”. In ad hoc mode, two or more WTRUs establish a communication among themselves without the need of a coordinating network element, i.e., base station. Ad hoc mode operation is illustrated in FIG. 1B. No access points to the network infrastructure are required. However, a base station can be configured with the ad hoc protocols to act as the other WTRUs in peer-to-peer communications. In such case, a base station may act as a bridge or a router to another network or to the Internet.
Where a base station does join an ad hoc network, it is treated as another WTRU and does not normally control the flow of communication. For example, FIG. 1B illustrates base station 54 in communication with WTRU 18 and WTRU 20 in an ad hoc network. In this scenario, the base station 54 does not control the flow of data.
Communications are normally limited to the other stations in an ad hoc network, but one WTRU may communicate indirectly with another WTRU via a third WTRU. For example, as shown in FIG. 1B, where both WTRU 22 and WTRU 24 are communicating in ad hoc mode with WTRU 26, communications may occur between WTRU 22 and WTRU 24. Additionally, when a WTRU is in ad hoc mode, it typically ignores infrastructure mode base station transmissions. It is also necessary for one WTRU to initiate ad hoc mode and other WTRUs to join in. The other stations will assimilate the operating parameter information as they join the ad hoc network.
The station that starts an ad hoc network selects the ad hoc network's operating parameters, such as the service set identifier (SSID), channel and beacon timing, and then transmits this information in, for example, beacon frames. As stations join the ad hoc network, they assimilate the operating parameters. In infrastructure mode, parameters such as the SSID are normally specified by a network controller connected to network base stations.
The SSID in an IEEE 802 based system can be a 32-character unique identifier attached to a header of packets sent over a WLAN. The SSID then acts as a password when a WTRU attempts to connect to a BSS or an independent BSS. The SSID differentiates one WLAN from another, so all base stations and all devices attempting to connect to a specific WLAN normally use the same SSID. A device will not normally be permitted to join a BSS unless it can provide the unique SSID.
In an IEEE 802 based system, once more than one station is part of an ad hoc network, all of the stations share the burden of sending beacon frames by a random distribution of that task to each station. Algorithms such as the spokesman election algorithm have been designed to “elect” one device as a master station (i.e., pseudo base station) of the ad hoc network with all others being slaves.
Various problems are common with open ad hoc networks which are essentially only self controlled. When a large number of WTRUs congregate in a small area, interference increases, thereby decreasing the throughput of all the WTRUs. In addition, when the overabundance of ad hoc wireless devices are concentrated in a hot spot area served by a base station of a WLAN, the communications between all such devices can be impeded since there are limits in frequency, channels, and bandwidth resources available for each wireless mode.
Another drawback of the open ad hoc networking is that it can affect the business model of a WLAN operator. The inventors have recognized that if peer-to-peer ad hoc mode communications are allowed without any overall control or monitoring, a WLAN operator loses revenue by not being able to charge for the WLAN infrastructure that is available and must be maintained even when it is not being used for infrastructure mode communications. It is therefore desirable to have a hybrid operational mode where peer-to-peer communications are controlled and/or monitored.
The inventors have recognized that other advantages can be gained through implementation of a hybrid ad hoc/infrastructure mode. For example, a mobile WTRU may travel into areas of poor signal quality where the communications with the network may become sporadic or nonexistent. In such cases, it would also be desirable if the WTRU can use a hybrid mode to relay communication through another WTRU which is in direct contact with a network base station.